The current use of multi-layer printed circuit boards with attendant high packaging densities has resulted in difficulties in the testing and diagnostic procedures associated with the completed board assemblies. For example, in an actual operative system, a large number of eight layer boards are utilized, each having many integrated circuit packages of the flat pack type. The latter have leads coming from the sides thereof and extending outward in substantially coplanar fashion with respect to the package surface. Normally, when installed, the leads extend outward a predetermined uniform distance, bend downward at right angles toward the board, and then extend a short distance parallel to the board. The last mentioned lead extremities are soldered to pads on the board. Because of the high density conditions, the printed circuit board pads are of minimal thickness and width. It is apparent that in contrast to the dual-in-line package which normally has leads disposed in apertures in the board and has mechanical rigidity, the flat pack depends upon the attachment of a narrow lead surface to a minimal pad area.
In the testing of completed printed circuit boards either immediately subsequent to fabrication or in the process of troubleshooting boards which have become defective during operation, the inter-board signals are available on input/output terminals associated with the board. Thus, no test problems are present since the terminals are readily accessed. However, in many situations, the intra-board signals which circulate exclusively within the board must be examined, and this presents some difficulty. One method of testing for the latter signals involves the soldering of the ends of individual wires to the respective points to be examined, such as the pads described previously. The other ends of the wires are then connected to test/diagnostic equipment. Such an operation requires that a highly skilled technician make the solder connections and be continuously available during testing. Moreover, since the wires between the board and the test equipment are relatively long, and the pad connections are tenuous at best, any accidental tugging of the wires may result in the pads being torn from the board surface. Since such boards are very expensive to fabricate, it is apparent that the test procedure may be counter-productive.
Another way of testing the intra-board signals, is to employ a typical hand held probe of the type used with oscilloscopes. Such a probe requires that the test technician exert extreme care to prevent the short circuiting of adjacent leads of the IC package. Additionally, if the probe is of the type that may be clipped to the lead, the same difficulty as noted hereinbefore with respect to damage to the board pads may be encountered. Finally, the use of such a probe does not permit the concurrent comparison of signals on adjacent leads of an IC package.
It is apparent that a need exists for a versatile, easy-to-use probe which completely eliminates the possibility of damage to the board or the IC packages. The present invention fills such a need.